A librarian whose remains were found in Edinburgh last month is thought to have passed through Hemel Hempstead on her way to Scotland.
Saima Ahmed, 36, was last seen boarding a train from Watford Junction to Northampton on August 30 last year.
She is then believed to have passed through Hemel and Birmingham before arriving in Scotland.
Her family reported her missing the following day, but her body was only found six months later.
Saima’s death is currently being treated as unexplained, and specially trained officers are providing support to the Ahmed family as inquiries progress.
Detective chief inspector Martin MacLean, head of crime operations for Edinburgh CID, said there was no evidence of crime but he could not ‘completely rule out criminality’.
Saima, who was living in Wembley, had no known links with Scotland and police are mystified as to how she died.
Mr MacLean said: “I urge any regular rail users who may have been on these services to please think carefully and to get in touch with Police Scotland on 101 if you remember, or spoke with, Saima.”
She was known to have left her Wembley home at around 8.30am, withdrew money from a local cash machine and boarded a train which took her to Watford Junction.
Police think she then got on the 11.06 train to Northampton which went on to Hemel Hempstead, Birmingham and through to Edinburgh, calling in at Wigan en route.
Officers are keen to speak to anyone who remembers Saima or who may have spoken to her to come forward.
She was described as an Asian female, around 5ft 5ins tall, medium build, with shoulder length straight dark hair. She was last seen wearing a dark long V-neck top, black trousers, black shoes and a black jacket.
Saima’s family said: “We, Saima’s family are extremely saddened and shocked by the death of Saima.
“She was a very loving and caring person who was part of a very close family.
“We are hoping someone can provide some information as to Saima’s journey on the 30th of August, 2015 and help us to understand what happened to her.”